This invention relates to a new fertilizer product in granular form, to a process for making it, and to a process for using it. More particularly, the invention relates to a granular fertilizer product in which the granules have strength, sizes, and weights suitable for mechanical dispensing and application to and into the soil. These new fertilizer granules provide a novel combination of fine particles of at least one source of nitrogen that is characterized by poor solubility in pH 7 water at ambient temperatures in the soil and by slow conversion in the soil to a form in which it is useful to plant life growing in the soil, together with a binder that binds the fine particles of this nitrogen source into granular form.
There is a continuing search and need for improved fertilizer materials. For example, while ammonium nitrate, containing 34% N, still ranks second only to ammonia, 86% N, as a source of fertilizer nitrogen, its use generally has been decreasing, in terms of market percentage, since 1965. The reason is the increased use of the higher nitrogen content materials, ammonia, with 82% N, and urea, with 46% N, respectively. The use of urea is a development of recent years, and may have been prompted in part by a desire to reduce shipping costs.
All of these nitrogen fertilizer materials just mentioned are readily soluble in water. They are therefore subject to leaching, and their use results in a rapid release of their nitrogen. Since this necessitates repeated applications for sustained growth, or one application with higher leaching losses, there have been many developments relating to slow release nitrogen fertilizer materials. Generally such materials sacrifice nitrogen content for some degree of control over nitrogen availability.
Melamine and its hydrolysis products, ammeline, ammelide, and cyanuric acid, have often been considered as potential sources of nitrogen for incorporation in fertilizer compositions or for utilization as nitrogen sources per se. Melamine has a nitrogen content of 66.6%, so that about two thirds of its weight is nitrogen. If it could be used as fertilizer material, it would obviously provide a good deal of nitrogen per unit weight applied. However, at present it is more expensive than urea. Moreover, commercially produced melamine is available only as a fine crystalline powder. It is manufactured in the form of very fine crystals because small size particles are required for the present commercial end markets for melamine, such as, for example, the production of melamine-formaldehyde resins and the production of fine retardant paints.
A typical screen analysis for one commercially available melamine, conducted with United States Standard Sieve screens, is as follows:
______________________________________ Percent Screen Analysis Retained ______________________________________ 40 Mesh 0-0.1 40-50 Mesh 0-0.1 50-60 Mesh 0-0.3 60-80 Mesh 0.5-5.0 80-100 Mesh 1.0-5.0 100-200 Mesh 13-30 200-325 Mesh 13-30 Thru 325 Mesh 40-60 ______________________________________
The commercially-produced small melamine crystals are desired by the resin producers because the small crystals dissolve more readily, and any larger particles, if present, would tend to require a longer processing time; therefore, the larger particles are less desirable. In the fine retardant paint market, the melamine crystals are dispersed in the paint, where the current fine particles sizes produce a smoother texture in the dried paint than would larger particles.
The fine particle sizes of the commercially available melamine products make melamine a product that is not very attractive for agricultural applications.
Moreover, the fine particles sizes of commercial melamine as currently produced, make it impractical to use as a fertilizer material. The fine particles, if applied to the surface of the ground, would be blown away by even mild winds. If applied by air, as from an airplane or helicopter, drifting would be a serious problem and would cause uneven application. If applied through mechanical applicators, the fine particles would tend to form bridges and thus would plug transfer and dispensing lines. These difficulties in handling the commercially available melamine solids would make any large scale agricultural application impractical. Nevertheless, there have been many investigations into the possible use of melamine as a fertilizer nitrogen source, generally on a small scale where the limitations imposed by the fine particle size of melamine were not a serious obstacle. However, in most cases, negative recommendations were generated, for reasons having little or nothing to do with melamine's fine particle size.
In 1937, as reported in Industrial and Engineering Chemistry 29, 202-205, Scholl and three associates working within the U.S. Department of Agriculture evaluated melamine sulfate, melamine phosphate and melamine nitrate in connection with the growth in pots of fine loamy sand of wheat and millet. These salts were compared with other nitrogen sources, including cyanuric acid, urea, and, used in combination, sodium nitrate and ammonium sulfate. The sulfate and phosphate salts of melamine were reported to be substantially less soluble than melamine itself, whereas melamine nitrate was said to be slightly more soluble than melamine at 29.degree. C. Melamine nitrate was considered to produce favorable results, but the results from the other two melamine salts were not so good. In pot growing tests with German millet and with Hungarian millet, the melamine nitrate salt gave the best results of the three melamine salts tested, and produced yields practically equivalent to those produced with control tests using urea and calcium cyanamide, but produced growth below that obtained with sodium nitrate. Finally, a series of nitrification tests were carried out with all three salts. The results obtained indicated that only about 1 % of the nitrogen content of the melamine was converted to nitrate in Norfolk loamy fine sand during a period of 13 weeks. This is in contrast to a conversion of 80% observed with ammonium sulfate. All in all, the results obtained seem to have been discouraging, particularly as to possible fertilizer use of melamine per se.
In 1941, some evaluations of melamine and melamine salts were carried out at Kyoto Imperial University, as reported in a Japanese publication, 15 J. Sci. Soil Manure, 559 (1941), in an article entitled, "Studies on the Fertilizing Value of Melamines and Guanidines". In a ten week experiment in paddy soil, it was found that melamine ammonified very slowly because biochemical degradation of melamine proceeds at a very slow rate in the soil. The conclusions of the authors were essentially negative with respect to the fertilizer use of melamine and its salts in connection with rice and barley. The authors concluded these crops did not respond in a positive way.
West German Pat. No. 926,853, in 1954, suggested the use of the melamine-formaldehyde resins as binding agents for granular fertilizer compositions also containing spent sulfite liquor and superphosphate. If field trials were made, they are not reported in the patent.
Very little nitrification of melamine was observed in a study by Clark et al. in 1957, as reported in Abstracts, 132nd Meeting, American Chemical Society, New York. Clark et al. reported that potassium and sodium cyanurates nitrified slowly for 6 weeks, followed by a more rapid and complete release of organic nitrogen between 6 and 9 weeks. Ammeline and mixtures of ammelide and ammeline nitrified at maximum rates between the 9- and 12-week incubation periods. Very little nitrification of melamine was observed over a 15-week period of incubation in soil media.
In 1961, T. G. Zarger published an article entitled, "Comparison of Slowly and Rapidly Available Nitrogen Fertilizers for Nursery Production of Pine Seedlings", in Tree Planters' Notes No. 66, pages 8-10. Zarger stated that there had been some interest in slow-dissolving fertilizer forms that might make nitrogen available over a longer period of time, as compared to the standard nitrogen sources that had been used in the nursery for the previous several decades. The author reported a comparison between ammonium nitrate, ammonium sulfate, sodium nitrate, urea, and diammonium phosphate, as standard, readily soluble nitrogen sources, with melamine, oxamide, ureaform, and magnesium ammonium phosphate, as slowly soluble or practically insoluble nitrogen sources. All of these fertilizers were applied to nursery beds prior to seeding, at a uniform rate of 100 pounds of nitrogen per acre. The tests were conducted with both loblolly pine and shortleaf pine. The results obtained seemed to indicate that all other nitrogen sources are preferable by far to melamine for the production of loblolly pine seedlings, with somewhat similar results for the production of shortleaf pine seedlings. For average height growth and survival, melamine performed poorly with respect to both loblolly pine and shortleaf pine. The results were not as good as those obtained over a two year period with ammonium nitrate. The author apparently doubted that any nitrogen was available to the seedlings from either melamine or oxamide, and concluded that the nursery tests did not show any of the poorly soluble nitrogen sources to be any better than standard ammonium nitrate.
In 1964, Hauck and Stephenson published an article in Agricultural and Food Chemistry 12, 147-151, describing the rate at which symmetrical triazines converted in the soil to a form useful to plants. For evaluation, melamine phosphate and melamine nitrate were recrystallized, respectively, washed, and dried. What the authors refer to as granules of melamine, acid, and metal ion were prepared by forming dried pastes of the several materials, then crushing and screening. Such materials included mixtures, for example, of melamine and phosphoric acid, melamine and nitric acid, and melamine and ferric ammonium sulfate. In addition, the performances of melamine, ammeline, ammelide, and cyanuric acid were evaluated in silty clay loam, in particle form, and melamine and cyanuric acid were evaluated in solution. Although some degradation of all was observed, the authors pointed out that melamine and cyanuric acid degraded at a faster rate than either particles having sizes in the range from -8+12 mesh, or solutions. The authors concluded with what appears to be a very negative observation, that the evaluation of these materials as slow-release nitrogen sources should be made only on crops that are expected to respond to small amounts of nitrogen added at frequent intervals. In addition, the authors reported that cyanuric acid is temporarily toxic to seedlings.
Also in 1964, Terman and several co-authors reported in Agricultural and Food Chemistry 12, 151-154 (1964) that they had evaluated urea and reagent grades of melamine, ammeline, ammelide, and cyanuric acid, for crops of corn forage and for crops of Coastal Bermuda grass, grown in greenhouse cultures. They confirmed that cyanuric acid was toxic initially. They found that urea and its pyrolyzate products were generally superior as to corn response, grass response, and also when evaluated in field experiments with wheat. The results can best be described as mixed with respect to the symmetrical triazines. Cyanuric acid was apparently considered a possible candidate for use if applied two weeks or more in advance of planting, to avoid the toxicity problem. Ammelide and ammeline, and urea pyrolysis products as well, were considered to be equal or superior to fertilizer-grade urea-formaldehyde resins as sources of nitrogen for Bermuda grass. They were also considered as possible nitrogen sources for use for tree and shrub fertilization. The findings with respect to melamine itself were generally negative. In the corn experiments, the authors measured nitrogen uptake and total dry weight, concluding that melamine did not supply an appreciable amount of nitrogen to the crop regardless of the amount of melamine applied. Measurements taken on the dry weight of Bermuda grass clippings indicated to the authors that no appreciable amount of nitrogen was supplied to the grass by melamine. In the field test with wheat, the authors measured the pounds per acre of dry forage, and found that small, insignificant increases in yields were obtained from melamine, the mean yields being only slightly higher than yields where no nitrogen source was applied at all. The authors concluded that melamine was only about 10% as effective as urea.
More recently, East German Pat. No. 120,645 described the use of a polymer coating on prilled urea to provide a slow-acting fertilizer. Prills having an average particle diameter of 1.7 mm. were pretreated with a coating substance or solution, dried, fluidized, and then coated with a latex polymer at 60.degree. C. Melamine was mentioned as one of the possible pretreating substances. The coated pellets had particle sizes in the range from 0.5-5 mm, preferably, 1-3 mm.
Even more recently, a publication in the Russian language reports results from an evaluation of melamine as a fertilizer in connection with one variety of spring barley: Markin et al., Tr. Slavrop S-kh Inst. 40(3), 65-67 (1977; CA 21454b (1979). As understood, the Russian investigators compared the degradation of melamine with other standard materials, including ammonium nitrate, in black earth (carbonate chernozem) from the Caucasus foothills. In addition, greenhouse tests were carried out in containers of the same soil. As might be expected from prior work, melamine at no point produced a nitrate level as high as that produced by ammonium nitrate.
The results reported are difficult to interpret. The control (background) apparently was fertilized with superphosphate. It is not clear whether the comparison trials using ammonium nitrate and melamine respectively had superphosphate in the soil or not. The composting experiment was run without the addition of fertilizer to the soil for the control. The spring barley greenhouse experiments apparently were run with the addition of superphosphate for the control experiment. In any case, the harvest, in the version with ammonium nitrate added, was at the same level as the control (background), according to the text. The trials with melamine were considered to produce "significantly higher" results both as to total harvest and as to grain harvest than with ammonium nitrate. Further, the author reports that melamine had a favorable long term effect, in that when all of the containers were planted again with spring barley, and observations of growth and development were continued up to the point where head formation occurred, there reportedly was an increase in the yield of barley, dry weight basis, as compared to the use of containers of the background type and of the type having background together with ammonium nitrate.
Because of the lack of details about experimental techniques and because of the very few trial runs made during the work that is reported, it is difficult to evaluate what was done by the Russian investigators and the conclusions that they reached.
U.S. Pat. No. 3,705,019, describes the production of granular cyanuric acid from fine cyanuric acid powder particles, to produce fast dissolving granules for treating the water in swimming pools. It has nothing to do with fertilizer.
Subsequently, Corte et al. in U.S. Pat. No. 4,083,712, produced nitrogenous fertilizers in the form of salts of a cation exchange resin. In Example 3 of the patent, a sulfonated polystyrene cross-linked with divinyl benzene, in the hydrogen form and strongly acidic, was reacted with an aqueous suspension of melamine. The reaction product was said to consist of 1000 ml. of a nitrogenous fertilizer containing 2.2 moles of melamine per liter. This material, and other ion exchange resin salts produced from guanidine and other nitrogen compounds, were tested over a two year period with grass in pots of loamy sandy soil which had received a basic dressing of phosphorus and potash. The first year grass yield is reported in the patent, although it is not clear what basis was used for determining the yield. All of the salts used produced results that seemed to be superior to those produced with control materials, after both one year and two year tests. In addition, based on the data reported, the melamine salt appears to have produced a superior yield to other salts, and to the control, after two years.
In what appears to be a subsequent development, described in South African Pat. No. 735,583, Corte and his associates pursued their investigations further. More work is described with nitrogenous fertilizer salt compositions comprising a cation exchange resin having a nitrogen base such as melamine chemically bound thereto. The cation exchanger optionally may be partially charged with a material such as melamine, and partially with inorganic nutrient ions. In Example E of this patent, a three year old lawn was used for testing different sources of long term fertilizer nitrogen. In one group of tests, the nitrogen was entirely furnished by a "conventional long-term" fertilizer, crotonylidenediurea (CDU). CDU is a condensation product of crotonaldehyde and urea. It is difficulty soluble in water. In a second, comparative test, the fertilizer was a mixture of 80% by weight of this long-term fertilizer material with 20% of a melamine ion exchange salt fertilizer. In a third test, the fertilizer nitrogen was supplied by a mixture of 60% of the long-term fertilizer material, crotonylidenediurea, with 40% of the melamine ion exchange salt fertilizer. The sum of the weights from five cuttings of this grass in grams per square meter was, for each of these three tests respectively: 1654; 1757; and 1899. Corte et al. observed that after 3 months, the conventional long term fertilizers evaluated were used up, whereas with the ion exchange salts, "no signs of exhaustion" were detectable after five months.
Both of these patents of Corte et al. point out that certain slow release nitrogen sources, such as urea-formaldehyde resins, have been combined with a short term nitrogen fertilizer material, such as a nitrate, to provide a greater initial fertilizing effect. Corte et al. observed, however, that melamine, unless chemically reacted to become the salt of an ion exchange resin, was "unsuitable for fertilizing purpose", U.S. Pat. No. 4,083,712, col. 2, lines 58-61.
The Allan Belgian Pat. No. 885,166, published Sept. 30, 1980, describes one way to improve the commercially available crystalline melamine for fertilizer use. The commercial product apparently contains one or more unidentified phytotoxic impurities. The impurities are removed by washing with room temperature water, at least once. The melamine, being very poorly soluble in water, remains in crystalline form, whereas the toxicant is more soluble and is carried off in the wash water. Tests reported in the Belgian patent demonstrate that the washed melamine has reduced toxicity as compared to its unwashed commercially available counterpart.
Because of the generally negative or equivocal results reported, based on the limited amount of work done to date with melamine, its related triazines, and their salts, little or no work has been done that has been concerned with the physical forms of these materials. On the contrary, the work done has been addressed to the question of whether these triazine compounds and their salts are in fact useful sources of nitrogen, and in general, the most frequent conclusion reached was that they were not. Consequently, apparently no one to date has taken the further step of trying to place these materials in a physical form that would permit their use in modern fertilizer application devices, or that would seek to optimize their performance if used. Perhaps such work has been inhibited by the knowledge that many substituted s-triazines are sufficiently toxic to plant life that several are used commercially as herbicides (see the Gysin et al. patents, for example, U.S. Pat. Nos. 2,909,420, 2,920,421, 2,923,614 and 2,936,227), and by the several reports as to the toxicity of the s-triazines themselves, as in the Allan Belgian Pat. No. 885,166, discussed above.